Dim polar light drove humans to evolve larger eyes

Humans evolved larger eye sockets as they moved towards the poles, allowing them to cope with the low light levels present compared with the tropics.

Eiluned Pearce and Robin Dunbar at the University of Oxford analysed 73 adult skulls belonging to people who lived at different latitudes. They found that both the overall skull volume and the volume of the eye socket increased with latitude, but the increase in eye socket volume – which is thought to relate to eyeball size – was larger than expected from the change in skull size alone.

Visual acuity – the ability to resolve fine detail – should be subtly worse at higher latitudes because of the dimmer light found there. But when the pair reviewed available data they found acuity was the same in populations at all latitudes. Pearce and Dunbar suggest their measured increase in eye socket volume, and inferred increase in eyeball size, could explain this.

"We were surprised to see how strong the effect was. Humans have only been in northern Europe for 40,000 years," says Dunbar.

Physical anthropologist Chris Kirk at the University of Texas at Austin thinks the idea is interesting, but is not convinced as the link between socket volume and eyeball size is relatively loose. To confirm the hypothesis "you would have to go back and measure the eyes", he says.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.